A cooled antenna device is described in Science, vol. 59, Feb. 5, 1993, pp. 793-795. Cooled antennas of normal-conducting material, such as copper, or superconducting material, particularly having an elevated superconductive (or transition) temperature T.sub.c of over 77 K, are distinguished over conventional copper antennas, which work at room temperature, by negligible inherent noise. Thus, they are intended for applications where the overall noise, which is generated by the noise from a transmitter, the antenna, and from an amplifier, is dominated by the antenna noise.
An example in the field of diagnostic medicine is the use of cooled antennas for detecting biomagnetic fields or field gradients, produced, for example, by the brain or the heart. Generally, a superconducting flux antenna is used for this purpose, which has associated superconducting electronics with SQUIDs (see, e.g., Applied Superconductivity, 1995, vol. 3, no. 7-10, pp. 399-423). Cooled antennas, in particular those that are superconducting, are also used in tomography, where the nuclear spin resonance (Nuclear Magnetic Resonance "NMR" or Magnetic Resonance Imaging "MRI") effect is utilized to receive high-frequency signals from the nuclear spin in the tissue of a patient (see, e.g., IEEE Trans. on Applied Supercond., Aug. 1992, vol. 3, no. 1, pp. 2450-2453, German Patent No. 42 18 635, or the text reference from Science mentioned above). The antennas to be placed directly on the patient are also often described as surface coils or surface antennas.
The above-mentioned Science article describes an antenna device of an NMR microscope, which, inside of a cryostat housing, has a chamber filled with liquid helium. Disposed within this chamber in an area proximate to the wall is an antenna of the high-T.sub.c -superconducting material YBa.sub.2 Cu.sub.3 O.sub.x (YBCO). The cryostat housing is configured to permit a proband (i.e. a test person), at room temperature, to be examined, who is to be positioned as closely as possible to the antenna. All parts in the vicinity of the antenna must be made of materials that have no adverse effect on the HF (high frequency) field to be detected.
An antenna device having an antenna of high-T.sub.c -superconducting material located in a chamber filled with liquid nitrogen is also described in U.S. Pat. No. 5,417,073.
Such a cooling technique using a liquid cryogenic medium is relatively expensive and not very desirable, particularly for routine use in a medical clinic, such as in nuclear spin tomography systems.